Actuator, optical scanner and image forming device

ABSTRACT

An actuator, includes: a movable plate; a supporter to support the movable plate; a pair of linking portions to link the movable plate and the supporter so as to allow the movable plate to rotate relative to the supporter; and a piezoelectric element to rotate the movable plate. The piezoelectric element elongated and contracted by an energization twists the pair of linking portions to rotate the movable plate, and each of the pair of the linking portions includes an axial member extending from the movable plate and a returned portion that links the axial member and the supporter and is formed so as to return to a side adjacent to the movable plate.

BACKGROUND

1. Technical Field

The present invention relates to an actuator, an optical scanner, and animage forming device.

2. Related Art

An optical scanner is known that uses an actuator including a twistvibrator and draws images by optical scanning in a laser printer or thelike. For example, refer to JP-A-2004-191953.

JP-A-2004-191953 discloses an actuator including a reflection mirror, afixing frame to support the reflection mirror, and a pair of springs tolink the both sides of the reflection mirror and the fixing frame. Eachspring includes a linking portion disposed apart from the reflectionmirror, a first spring linking the reflection mirror and the linkingportion, and a second spring linking the linking portion and the fixingframe at a side opposite to the first spring.

Such actuator is heated by surrounding temperature or light irradiatedto the reflection mirror, for example. As a result, the first springthermally expands. That is, a pair of the first springs is elongated inthe longitudinal direction (a direction, in parallel with a rotationcenter axis, being apart from the reflection mirror) by thermalexpansion.

However, in the actuator disclosed in JP-A-2004-191953, the displacementof each linking portion in a direction, in parallel with the rotationcenter axis and apart from the reflection mirror, is hindered by thesecond spring. This causes each first spring to be displaced (e.g. bebent or buckle) from a desired position so as to reduce the deformationdue to thermal expansion, and the reflection mirror is displaced in itsthickness direction. This displacement results in the rotation centeraxis of the reflection mirror being shifted. As a result, desiredrotation characteristics cannot be achieved.

In addition, when the actuator disclosed in JP-A-2004-191953 is used foran optical scanner, light reflected by the reflection mirror cannot bescanned to a desired position of an object, since an optical path lengthfrom a light source to the reflection mirror is changed due to therotation center axis shift of the reflection mirror. That is, it isdifficult to perform a desired scanning characteristic.

SUMMARY

An advantage of the invention is to provide an actuator, an opticalscanner, and an image forming device that can perform a desiredvibration characteristic by reducing or eliminating influences due toenvironmental temperature with achieving miniaturization.

According to a first aspect of the invention, an actuator includes: amovable plate; a supporter to support the movable plate; a pair oflinking portions linking the movable plate and the supporter so as toallow the movable plate to rotate relative to the supporter; and apiezoelectric element to rotate the movable plate. The piezoelectricelement elongated and contracted by an energization twists the pair oflinking portions to rotate the movable plate. Each of the pair of thelinking portions includes an axial member extending from the movableplate and a returned portion that links the axial member and thesupporter, and is formed so as to return to a side adjacent to themovable plate. As a result, the actuator can be provided that can reduceor eliminate influences due to environmental temperature and perform adesired vibration characteristic.

It is preferable that each returned portion include a pair of elasticmembers that has an elongation shape and be capable of being elasticallydeformed and be provided so as to face each other across a rotationcenter axis of the movable plate. It becomes easy to maintain therotation center axis of the movable plate constant even when thermalexpansion occurs.

It is preferable that each returned portion include a driving memberlinking the axial member and each elastic member, and each elasticmember be provided closer to the movable plate than the driving member.Accordingly, the movable plate can provide a larger rotation.

It is preferable that an elongation direction of each elastic member bein parallel with the rotation center axis of the movable plate. As aresult, the driving member can be displaced smoothly when thermalexpansion occurs.

It is preferable that a separation distance between the pair of elasticmembers gradually decrease from a side adjacent to the movable plate toa side adjacent to the driving member. The movable plate can provide alarger rotation with achieving miniaturization.

It is preferable that a separation distance between the pair of elasticmembers gradually increase from a side adjacent to the movable plate toa side adjacent to the driving member. The movable plate can provide alarger rotation with achieving miniaturization. In addition, theactuator can improve its response property.

It is preferable that the piezoelectric element be bonded to eachelastic member in a longitudinal direction of the elastic member and beelongated and contracted in the longitudinal direction of thecorresponding elastic element to bend the elastic member. This structureallows each elastic member to be uniformly bent entirely along thelongitudinal direction. As a result, each elastic member can beefficiently bent with reducing stress applied to.

It is preferable that each piezoelectric element have a width largerthan a width of the elastic member on which the piezoelectric element isbonded and be bonded so as to entirely cover the elastic member in awidth direction of the elastic member. The elastic member can be greatlybent. In addition, manufacturing the actuator can be simplified.

It is preferable that the piezoelectric element be provided tocorrespond to each elastic member, and an end in anelongation-contraction direction of each piezoelectric element touch thecorresponding elastic member, and an elongation-contraction of thepiezoelectric element bend the elastic member. This structure allowslarge driving force to be transferred to each elastic member by theelongation-contraction of the piezoelectric element.

It is preferable that the piezoelectric element be bonded to an end inan elongation direction of the elastic member and serve as thesupporter, and the end be located at a side opposite to the drivingmember. Accordingly, the actuator can be miniaturized.

It is preferable that each elastic member include a first elastic memberand a second elastic member having a separation distance smaller than aseparation distance of the first elastic element relative to the axialmember, and the piezoelectric element be bonded to the first elasticmember, and an elongation-contraction of the piezoelectric element in alongitudinal direction of the first elastic member bend the firstelastic member to twist the second elastic member to displace thedriving member. Accordingly, the actuator can be provided with low costssince the minimal number of piezoelectric elements is needed.

It is preferable that the second elastic member be provided in avicinity of the rotation center axis. This structure allows the shape ofthe pair of axial members to be simplified and the rotation center axisshift of the movable plate to be suppressed.

It is preferable that the movable plate have a light reflector havinglight reflection property on a plate surface thereof. The actuator canbe used for optical devices.

According to a second aspect of the invention, an optical scannerincludes: a movable plate provided with a light reflector having lightreflection property; a supporter to support the movable plate; a pair oflinking portions linking the movable plate and the supporter so as toallow the movable plate to rotate relative to the supporter; and apiezoelectric element to rotate the movable plate. The piezoelectricelement elongated and contracted by an energization twists the pair oflinking portions to rotate the movable plate to scan light reflected bythe light reflector. Each linking portion includes an axial memberextending from the movable plate and a returned portion that links theaxial member and the supporter, and is formed so as to return to a sideadjacent to the movable plate.

As a result, the optical scanner can be provided that can reduce oreliminate influences due to environmental temperature and perform adesired vibration characteristic.

According to a third aspect of the invention, an image forming deviceincludes an optical scanner that includes: a movable plate provided witha light reflector having light reflection property; a supporter tosupport the movable plate; a pair of linking portions linking themovable plate and the supporter so as to allow the movable plate torotate relative to the supporter; and a piezoelectric element to rotatethe movable plate. In the scanner, the piezoelectric element elongatedand contracted by an energization twists the pair of linking portions torotate the movable plate to scan light reflected by the light reflector.Each linking portion includes an axial member extending from the movableplate and a returned portion that links the axial member and thesupporter, and is formed so as to return to a side adjacent to themovable plate.

As a result, the image forming device can be provided that can reduce oreliminate influences due to environmental temperature and perform adesired vibration characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view illustrating an actuator of a firstembodiment of the invention.

FIG. 2 is a sectional view taken along a line A-A of FIG. 1.

FIGS. 3A and 3B show an example of a waveform of voltage applied to apiezoelectric element included in the actuator shown in FIG. 1.

FIG. 4 is a top view illustrating an actuator of a second embodiment ofthe invention.

FIG. 5 is a sectional view taken along a line B-B in FIG. 4.

FIG. 6 is a top view illustrating an actuator of a third embodiment ofthe invention.

FIG. 7 is a sectional view taken along a line C-C in FIG. 6.

FIG. 8 is an enlarged view of a piezoelectric element included in theactuator shown in FIG. 6.

FIGS. 9A and 9B show an example of a waveform of voltage applied to apiezoelectric element included in the actuator shown in FIG. 6.

FIG. 10 is a top view illustrating an actuator of a fourth embodiment ofthe invention.

FIG. 11 is a sectional view taken along a line D-D in FIG. 10.

FIG. 12 is a top view illustrating an actuator of a fifth embodiment ofthe invention.

FIG. 13 is a top view illustrating an actuator of a sixth embodiment ofthe invention.

FIG. 14 is a top view illustrating an actuator of a seventh embodimentof the invention.

FIGS. 15A and 15B are sectional views taken along a line E-E of FIG. 14.

FIG. 16 is a schematic view illustrating an image forming device usingan optical scanner of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of an actuator, an optical scanner, and an image formingdevice will be described with reference to accompanying drawings.

First Embodiment

A first embodiment of the actuator will be described.

FIG. 1 is a perspective view of the actuator of the first embodiment.FIG. 2 is a sectional view taken along the line A-A in FIG. 1. FIGS. 3Aand 3B show an example of a waveform of voltage applied to apiezoelectric element included in the actuator shown in FIG. 1. Forexpository convenience, the front side, the rear side, the right side,and the left side in FIG. 1 are described as “up,” “down or low,”“right,” and “left” respectively. Likewise, the top side, the bottomside, the right side, and the left side in FIG. 2 are described as “up,”“down or low,” “right,” and “left” respectively.

An actuator 1 includes a base 2 having a two-degree of freedom vibrationsystem as shown in FIG. 1, and a support substrate 3 supporting the base2 with a bonding layer 4 interposed therebetween.

The base 2 is provided with a movable plate 21, a supporter 22 tosupport the movable plate 21, a pair of linking portions 23 and 24 tolink the movable plate 21 and the supporter 22, as shown in FIG. 1.

The portion 23 includes an axial member 231 extending from the movableplate 21, and a returned portion 232, which links the axial member 231and the supporter 22 and is formed so as to be returned to a sideadjacent to the movable plate 21. The returned portion 232 is composedof a driving member 233 connected to one end (opposite to the other endconnected to the movable plate 21) of the axial member 231 along thelongitudinal direction, and a pair of elastic members 234 and 235, bothof which link the driving member 233 and the supporter 22.

The linking portion 24 includes an axial member 241 extending from themovable plate 21, and a returned portion 242, which links the axialmember 241 and the supporter 22 and is formed so as to be returned to aside adjacent to the movable plate 21. The returned portion 242 iscomposed of a driving member 243 connected to one end (opposite to theother end connected to the movable plate 21) of the axial member 241along the longitudinal direction, and a pair of elastic members 244 and245, both of which link the driving member 243 and the supporter 22.

That is, the base 2 includes the movable plate 21, the supporter 22, theaxial members 231 and 241, the driving members 233 and 243, and theelastic members 234, 235, 244, and 245. Each of them will now bedescribed sequentially.

The movable plate 21 has a plate shape. A light reflector 211 havinglight reflection property is disposed on the upper surface of themovable plate 21. A pair of driving members 233 and 243 is disposed soas to face each other across the movable plate 21 in a plan view whenthe movable plate 21 is in an un-driven state (hereinafter, the view isreferred to as a “plan view of the movable plate 21.”

Each of driving members 233 and 243 has a plate shape. The pair ofdriving members 233 and 243 is symmetrically disposed relative to themovable plate 21 as shown in FIG. 1. The driving members 233 and 243have the same shape and dimensions. However, the shape of the pair ofdriving members 233 and 243 is not particularly limited. They also maynot have the same shape and dimensions.

The driving member 233 is linked to the movable plate 21 with the axialmember 231 interposed therebetween while the driving member 243 islinked to the movable plate 21 with the axial member 241 interposedtherebetween.

Each of axial members 231 and 241 has an elongated shape and iselastically deformable. The axial member 231 links the movable plate 21and the driving member 233 so as to allow the movable plate 21 to rotaterelative to the driving member 233. Likewise, the axial member 241 linksthe movable plate 21 and the driving member 243 so as to allow themovable plate 21 to rotate relative to the driving member 243.

The pair of axial members 231 and 241 is coaxially disposed. The movableplate 21 rotates about the axis (rotation center axis X).

The supporter 22 is formed so as to surround the circumference of themovable plate 21 and the pair of driving members 233 and 243 in the planview of the movable plate 21. The supporter 22 includes a frame 221having a frame shape, and protrusions 222, 223, 224, and 225 thatprotrude from the frame 221 inwardly into a space defined by the frame221.

In a direction in parallel with the rotation axis X, a left side portionof the frame 221 and the driving member 233 creates a gap while a rightside portion of the frame 221 and the driving member 243 creates anothergap. The gaps are formed so as to tolerate each displacement of thedriving members 233 and 243 due to thermal expansion.

The protrusions 222 and 223 are disposed between the movable plate 21and the driving plate 233. The protrusions 222 and 223 are alsosymmetrically disposed relative to the rotation center axis X and so asto face each other across the rotation center axis X in the plan view ofthe movable plate 21. The protrusion 222 is linked to the driving member233 with the elastic member 234 interposed therebetween while theprotrusion member 223 is linked to the driving member 233 with theelastic member 235 interposed therebetween.

The protrusions 224 and 225 are disposed between the movable plate 21and the driving member 243. The protrusions 224 and 225 are alsosymmetrically disposed relative to the rotation center axis X and so asto face each other across the rotation center axis X in the plan view ofthe movable plate 21. The protrusion 224 is linked to the driving member243 with the elastic member 244 interposed therebetween while theprotrusion member 225 is linked to the driving member 243 with theelastic member 245 interposed therebetween.

The shape of the supporter 22 is not limited as long as it can supportsthe movable plate 21 with the linking portions 23 and 24 so as to allowthe movable plate 21 to rotate. For example, the frame 221 may beseparated into a left part and a right part in FIG. 1, not having aframe shape, and further may be omitted. In addition, a particular shapeof the frame 221 may omit the protrusions 222 to 225.

Each of the elastic members 234, 235, 244, and 245 has an elongatedshape and is elastically deformable. Each of elastic members 234, 235,244, and 245 extends in a direction in parallel with the rotation centeraxis X.

The elastic member 234 links the driving member 233 and the protrusion222 while the elastic member 235 links the driving member 233 and theprotrusion 223. Likewise, the elastic member 244 links the drivingmember 243 and the protrusion 224 while the elastic member 245 links thedriving member 243 and the protrusion 225.

Each of the pair of elastic members 234 and 235 is disposed closer tothe movable plate 21 than the driving member 233. The pair of elasticmembers 234 and 235 is also symmetrically disposed relative to therotation center axis X and so as to face each other across the rotationcenter axis X in the plan view of the movable plate 21.

Likewise, each of the pair of elastic members 244 and 245 is disposedcloser to the movable plate 21 than the driving member 243. The pair ofelastic members 244 and 245 is also symmetrically disposed relative tothe rotation center axis X and so as to face each other across therotation center axis X in the plan view of the movable plate 21.

Thus, the actuator 1 can be miniaturized since the elastic members 234and 235 are disposed closer to the movable plate 21 than the drivingmember 233 while the elastic members 244 and 245 are disposed closer tothe movable plate 21 than the driving member 243. In addition, thisstructure can reduce influence or eliminate influences due toenvironmental temperature to show and maintain a desired vibrationcharacteristic, as will be described later.

A piezoelectric element 51, which will be described later, is bonded onthe upper surface of the elastic member 234. Likewise, a piezoelectricelement 52 is bonded on the upper surface of the elastic member 235, apiezoelectric element 53 is bonded on the upper surface of the elasticmember 244, and a piezoelectric element 54 is bonded on the uppersurface of the elastic member 245. The piezoelectric elements 51 to 54are a driving source to rotate the movable plate 21 about the rotationcenter axis X.

The base 2 is structured as above described and included in the actuator1. In the actuator 1, the piezoelectric elements 51 and 52 elongated andcontracted by an energization bend the pair of elastic members 234 and235 in the thickness direction of the movable plate 21, rotating thedriving member 233 about the rotation center axis X. Likewise, thepiezoelectric elements 53 and 54 elongated and contracted by anenergization bend the pair of elastic members 244 and 245 in thethickness direction of the movable plate 21, rotating the driving member243 about the rotation center axis X. As a result, rotating the pair ofdriving members 233 and 243 twists each of the pair of axial members 231and 241, rotating the movable plate 21 about the rotation center axis X.

Accordingly, the base 2 has two vibration systems: a first vibrationsystem composed of the elastic members 234, 235, 244, and 245, and thepair of driving members 233 and 243; and a second vibration systemcomposed of the pair of axial members 231 and 241, and the movable plate21. That is, the actuator 1 has two-degree-of-freedom vibration systemcomposed of the first vibration system and the second vibration system.

The base 2 is, for example, mainly made of silicon. In this case, themovable plate 21, the axial members 231 and 241, the driving members 233and 243, the elastic members 234, 235, 244, and 245, and the support 22(frame 221 and the protrusions 222 to 225) are integrally formed. Theuse of silicon as a main material can achieve superior durability aswell as superior rotation characteristics. The material also enables thebase to be finely processed. Thus, the actuator 1 can be miniaturized.

The base 2 may include the movable plate 21, the supporter 22, the axialmembers 231 and 241, the driving members 233 and 243, and the elasticmembers 234, 235, 244, and 245 all of which are formed from a substratehaving a multilayered structure, such as SOI substrates. In this case,the movable plate 21, the supporter 22, the axial members 231 and 241,the driving members 233 and 243, and the elastic members 234, 235, 244,and 245 are preferably integrally formed from one layer of themultilayered substrate.

Such base 2 is bonded to the support substrate 3 with the bonding layer4 interposed therebetween.

The support substrate 3 is, for example, mainly made of glass, silicon,or SiO₂. The support substrate 3 is formed in a frame shape coincidingwith the shape of the support 22 in the plan view of the movable plate21.

The shape of the support substrate 3 is not particularly limited as longas it can support the base 2 without hindering the vibration system frombeing driven. For example, the bottom (opposite to the base 2) of thesupport substrate 3 may not be opened. That is, the support substrate 3may have a recess in the upper surface. In addition, a particular shapeof the frame 22 may omit the support substrate 3.

The bonding layer 4, which is formed between the support substrate 3 andthe base 2, is, for example, mainly made of glass, silicon, or SiO₂. Thebonding layer 4 may be omitted. That is, the base 2 and the supportsubstrate 3 may be directly bonded.

Next, the piezoelectric elements 51 to 54 will be described that serveas a driving source to rotate the movable plate 21. Since thepiezoelectric elements 51 to 54 have the same structure, only thepiezoelectric element 52 will be representatively described. Thedescription of the piezoelectric elements 51, 53, and 54 is omitted.

The piezoelectric element 52 is bonded to the elastic member 235 so asto cover the entire upper surface of the elastic member 235 and acrossthe border of the elastic member 235 and the supporter 22 (theprotrusion 223). The piezoelectric element 52 is also coupled to a powersupply circuit (not shown), which energizes the piezoelectric element 52to be elongated and contracted in the longitudinal direction of theelastic member 235.

The piezoelectric element 52 includes a piezoelectric layer 521 mainlymade of a piezoelectric material, and a pair of electrodes 522 and 523that sandwich the piezoelectric layer 521 as shown in FIG. 2.

Examples of piezoelectric materials used for the piezoelectric layer 521include zinc oxide, aluminum nitride, lithium tantalite, lithiumniobate, potassium niobate, lead zirconate titanate (PZT), and bariumtitanate. One or more than one in mixture of the above can be used.Particularly, one mainly containing at least one of zinc oxide, aluminumnitride, lithium tantalite, lithium niobate, potassium niobate, and leadzirconate titanate (PZT) is preferably used. With the piezoelectriclayer 521 made of such material, the actuator 1 can be driven at higherfrequency.

The electrode 522 is formed so as to cover the entire area under thepiezoelectric layer 521 and expose a part thereof on the protrusion 223.The electrode 522 is bonded to the elastic member 235 and the protrusion223.

On the other hand, the electrode 523 is formed so as to cover the entireupper surface of the piezoelectric layer 521. The electrode 523 isconnected to a terminal 524 disposed on the protrusion 223 with a wiringwire formed by wire bonding, for example.

Material to form the electrodes 522 and 523 (the terminal 524) is notparticularly limited as long as it has conductivity.

The piezoelectric element 52 may be directly formed on the elasticmember 235 by a thin film forming method such as CVD, sputtering, ahydrothermal synthesis method, a sol-gel method, and a fine-particlespraying method. An individually manufactured piezoelectric element(e.g. a bulk element) may be bonded on the elastic member 235 (the base2) with a resin material (adhesive) or the like.

The structure of the piezoelectric element 52 is not limited to theabove described as long as it can be elongated and contracted in thelongitudinal direction of the elastic member 235. For example, theterminal 524 may not be formed on the protrusion 223 or may be omitted.

The actuator 1 is driven as follows.

For example, a voltage shown in FIG. 3A is applied to the piezoelectricelements 51 and 53 while a voltage shown in FIG. 3B is applied to thepiezoelectric elements 52 and 54. That is, the following two states arealternately repeated: a first state in which voltage is applied to thepiezoelectric elements 51 and 53; and a second state in which voltage isapplied to the piezoelectric elements 52 and 54.

Since the linking portions 23 and 24 show the same torsion-deformation,the torsion-deformation of the linking portion 23 will berepresentatively described. The description of the torsion-deformationof the linking portion 24 is omitted.

First, the first state will be described. The piezoelectric element 51is elongated by an energization, resulting in an end portion, adjacentto the driving member 233, of the elastic member 234 in its longitudinaldirection being displaced downwardly (to the support substrate 3). Incontrast, an end portion, adjacent to the driving member 233, of theelastic member 235 in its longitudinal direction is displaced upwardly(to a side opposite to the support base 3) by a reaction of the bendingdeformation of the elastic member 234.

As a result, one portion, adjacent to the elastic member 234 relative tothe rotation center axis X, of the driving member 233 is displaceddownwardly while the other portion, adjacent to the elastic member 235relative to the rotation center axis X, of the driving member 233 isdisplaced upwardly. Consequently, the driving member 233 tilts about therotation center axis X.

Next, the second state will be described. The piezoelectric element 52is elongated by an energization, resulting in an end portion, adjacentto the driving member 233, of the elastic member 235 in its longitudinaldirection being displaced downwardly. In contrast, an end portion,adjacent to the driving member 233, of the elastic member 234 in itslongitudinal direction is displaced upwardly by a reaction of thebending deformation of the elastic member 235.

As a result, one portion, adjacent to the elastic member 235 relative tothe rotation center axis X, of the driving member 233 is displaceddownwardly while the other portion, adjacent to the elastic member 234relative to the rotation center axis X, of the driving member 233 isdisplaced upwardly. Consequently, the driving member 233 tilts about therotation center axis X.

The above alternative repetition bends the pair of elastic members 234and 235 in an opposite direction each other, allowing the driving member233 to rotate about the rotation center axis X. The rotation of thedriving member 233 twists the axial member 231, allowing the movableplate 21 to rotate about the rotation center axis X.

In the embodiment, the movable plate 21 is rotated by alternatelyrepeating two conditions: the first state in which voltage is applied tothe piezoelectric elements 51 and 53, and the second state in whichvoltage is applied to the piezoelectric elements 52 and 54. However, themethod is not particularly limited to this as long as it can rotate themovable plate 21. For example, an alternative voltage having a180-degree different phase (i.e. opposite phase) may be intermittentlyapplied to the piezoelectric elements 51 and 53, and the piezoelectricelements 52 and 54.

The structure of the actuator 1 has been described in detailhereinabove.

The actuator 1 may be heated with heat supplied, resulting in the axialmembers 231 and 241 being thermally expanded. The causes of the thermalexpansion include surrounding temperature change, and heat produced bythe actuator 1 in itself.

The actuator of the embodiment particularly uses the piezoelectricelement as a driving source that produces heat by an energization. Theheat produced by the piezoelectric element causes the thermal expansionof the actuator 1.

In another case in which the actuator 1 is used for an optical scanner,part of light irradiated to the light reflector 211 is converted intoheat without being reflected. As a result, the actuator 1 is thermallyexpanded.

This thermal expansion induces particularly each of the axial members231 and 241 having an elongated shape, and the elastic members 234, 235,244, and 245 having an elongated shape to extend in its longitudinaldirection.

Here, the pair of elastic members 234 and 235 is disposed closer to themovable plate 21 than the driving member 233 in the actuator 1 (thelinking portion 24 also shows the same). Thus, even when the axialmembers 231 and 241 are thermally expanded, the rotation center axis Xcan be kept constant at a desired position with tolerating the thermaldeformation. That is, the movable plate 21 can be prevented from beingdisplaced in its thickness direction.

Specifically, when the axial member 231 thermally expands, the axialmember 231 extends its length in the longitudinal direction. In otherwords, the axial member 231 extends in the longitudinal direction as thetemperature of the axial member 231 increases.

On the other hand, the driving member 233 is displaced so as to be apartfrom the movable plate 21 by the thermal expansion of each of theelastic members 234 and 235. This displacement of the driving member 233allows the axial member 231 to be deformed by thermal expansion (i.e.,elongation in the longitudinal direction).

The actuator 1 can reduce the displacement of the movable plate 21 inits thickness direction when the axial member 231 thermally expands. Asa result, the actuator 1 can rotate the movable plate 21 while therotation center axis X is kept constant even when thermal expansionoccurs, performing a desired vibration characteristics.

When the actuator 1 is used for an optical scanner, an optical pathlength (separation distance) from a light source to the light reflector211 and an optical path length (separation distance) from the lightreflector 21 to a scanning object can be kept at a desired distance. Asa result, the actuator 1 can maintain a desired scan characteristic evenwhen thermal expansion occurs.

In the actuator 1, the pair of elastic members 234 and 235 issymmetrically disposed relative to the rotation center axis X and so asto face each other across the rotation center axis X. Because of thisstructure, the rotation center axis X is easily kept constant at adesired position even when each of the axial member 231 and the elasticmembers 234 and 235 is thermally expanded.

In addition, in the actuator 1, the pair of elastic members 234 and 235is disposed so that each longitudinal direction is in parallel with thelongitudinal direction of the axial member 231. As a result, when eachof the axial member 231 and the elastic members 234 and 235 is thermallyexpanded, the driving member 233 can be easily displaced so as to beapart from the movable plate 21.

In the embodiment, the piezoelectric elements 51 to 54 are used as adriving source to rotate the movable plate 21. Since the piezoelectricelement produces heat by an energization, the above effects are furtherenhanced by combining the piezoelectric elements 51 to 54 and the base2.

Second Embodiment

Next, an actuator according to a second embodiment of the invention willbe described.

FIG. 4 is a top view illustrating the actuator of the second embodiment.FIG. 5 is a sectional view taken along the line B-B in FIG. 4. Forexpository convenience, the top side in FIG. 5 is described as “up,”while the bottom side is described as “down or low.”

The following description of an actuator 1A of the second embodimentfocuses primarily on differences from the actuator 1 of the firstembodiment, and similar points will be omitted.

The actuator 1A of the second embodiment is nearly the same as theactuator 1 of the first embodiment except for the shapes of thepiezoelectric elements 51A to 54A. The same numeral is given to the samestructure of the first embodiment.

Since the piezoelectric elements 51A to 54A have the same structure,only the piezoelectric element 51A will be representatively described.The description of the piezoelectric elements 52A to 54A is omitted.

The piezoelectric element 51A has a width larger than the width (thelength perpendicular to the rotation center axis X in the plan view ofthe movable plate 21) of the elastic member 234 and is bonded to theelastic member 234 so as to entirely cover the elastic member 234 in itswidth direction.

The piezoelectric element 51A having a width larger than that of theelastic member 234 can transfer a desired driving force to the elasticmember 234 by being elongated and contracted (i.e. a desired bendingdeformation amount of the elastic member 234 is achieved) when thepiezoelectric element 51A is bonded so as to entirely cover the elasticmember 234 in its width direction even if the bonding position of thepiezoelectric element 51A to the elastic member 234 is shifted from thepredetermined position in the width direction of the elastic member 234in manufacturing the actuator 1.

As a result, the manufacturing of the actuator 1A can be simplified andits mounting time (manufacturing time) can be reduced since a desiredvibration characteristic can be performed without a fine adjustment of abonding position when the piezoelectric element 51A is bonded to theelastic member 234. Such effect is specifically enhanced when a processis included in which the piezoelectric element 51A is manufacturedseparately from the base 2, and then the piezoelectric element 51A isbonded to the elastic member 234 with a resin material (adhesive) or thelike interposed therebetween.

The piezoelectric elements 52A to 54A also have the same shape and aredisposed in the same manner. The use of the piezoelectric elements 51Ato 54A allows each bending deformation amount of the elastic members234, 235, 244, and 245 to be nearly equalized with extreme ease.

The second embodiment can achieve the same effects of the firstembodiment.

Third Embodiment

Next, an actuator according to a third embodiment of the invention willbe described.

FIG. 6 is a top view illustrating the actuator of the third embodiment.FIG. 7 is a sectional view taken along the line C-C in FIG. 6. FIG. 8illustrates a piezoelectric element. FIGS. 9A and 9B illustrates anexample of voltage applied to the piezoelectric element. For expositoryconvenience, the top side in FIG. 7 is described as “up,” while thebottom side is described as “down or low.”

The following description of an actuator 1B of the third embodimentfocuses primarily on differences from the actuator 1 of the firstembodiment, and similar points will be omitted.

The actuator 1B of the third embodiment is nearly the same as theactuator 1 of the first embodiment except for the structures andarrangements of the piezoelectric elements 55 to 58, and the structureof the support substrate 3. The same numeral is given to the samestructure of the first embodiment.

A support substrate 3B includes a base 31 having a plate shape and awall 32 that is bonded to the upper surface of the base 31 and formed soas to coincide with the shape of the supporter 22 in the plan view ofthe movable plate 21.

On the upper surface of the base 31, the piezoelectric element 55 isbonded to a portion facing the elastic member 234, the piezoelectricelement 56 is bonded to a portion facing the elastic member 235, thepiezoelectric element 57 is bonded to a portion facing the elasticmember 244, and the piezoelectric element 58 is bonded to a portionfacing the elastic member 245.

Since the piezoelectric elements 55 to 58 have the same structure andsame arrangement, only the piezoelectric element 55 will berepresentatively described. The description of the piezoelectricelements 56 to 58 is omitted.

The piezoelectric element 55 is bonded to the base 31 of the supportsubstrate 3 at its lower end surface, and bonded to the lower surface ofthe elastic member 234 at its upper surface in the thickness directionof the movable plate 21 (i.e. an up-and-down direction in FIG. 7). Thepiezoelectric element 55 is elongated and contracted in the thicknessdirection of the movable plate 21 (i.e. the direction indicated by adouble-ended arrow in FIG. 7).

The piezoelectric element 55 includes a plurality of piezoelectriclayers 551 and a plurality of electrode layers 552 to supply voltage toeach of the plurality of piezoelectric layers 551. Each piezoelectriclayer 551 and each of the plurality of electrode layers 552 arealternately layered in the thickness direction of the movable plate 21.That is, the piezoelectric element 55 is a layered piezoelectric elementelongated and contracted in the thickness direction of the movable plate21. The piezoelectric element 55 can provide a large displacement amountwhile the driving voltage is reduced.

The piezoelectric layers 551 are formed so that each piezoelectric layer551 has a polarization direction different from the adjacent one. Thatis, the polarization direction of the piezoelectric layer 551 oddnumbered layer from the base 31 side is opposite to the polarizationdirection of the piezoelectric layer 551 even numbered layer from thebase 31 side. This structure allows the piezoelectric element 55 morereliably to provide a larger displacement amount while the drivingvoltage is reduced. In the specification, the term “polarizationdirection” means a direction directing from one surface in whichnegative charges excessively exist to the other surface in whichpositive charges excessively exist of the piezoelectric layer, whenexcessive negative charges exist in the one surface while excessivepositive charges exist in the other surface (in a case of intrinsicpolarization or residual polarization) in a state of applying noelectric field and stress to the piezoelectric layer.

Each electrode layer 552 is interposed between the piezoelectric layers551 adjacent each other. The electrode layers 552 are formed so as toprovide an overlapped region (an active region) of two electrodes layers552 adjacent each other. The electrode layer 552 odd numbered layer fromthe base 31 side is connected to a common electrode 553 disposed on theside face of the piezoelectric element 55 while the electrode layer 552even numbered layer from the base 31 side is connected to a commonelectrode 554 disposed on the face, opposite to the face on which thecommon electrode 553 is disposed, of the piezoelectric element 55.

Voltage is applied to each piezoelectric layer 551 in the overlappedregion by applying voltage between the common electrodes 553 and 554. Asa result, each piezoelectric layer 551 is elongated and contracted inthe thickness direction of the movable plate 21.

The structure of the piezoelectric element 55 is not particularlylimited as long as it can be elongated and contracted in the thicknessdirection of the movable plate 21. The common electrodes 553 and 554 maynot be disposed on the side faces of the piezoelectric element 55. Forexample, they may be formed to the base 31.

The actuator 1B provided with the piezoelectric elements 55 to 58 canrotate the movable plate 21 as follows, as an example.

For example, a voltage shown in FIG. 9A is applied to the piezoelectricelements 55 and 57 while a voltage shown in FIG. 9B is applied to thepiezoelectric elements 56 and 58. That is, two voltages each having a180-degree phase difference from the other are applied to thepiezoelectric elements 55 and 57, and the piezoelectric elements 56 and58. As a result, the following two states are alternately repeated: afirst state in which the piezoelectric elements 55 and 57 are elongatedwhile the piezoelectric elements 56 and 58 are contracted; and a secondstate in which the piezoelectric elements 55 and 57 are contracted whilethe piezoelectric elements 56 and 58 are elongated.

Next, deformations of the linking portions 23 and 24 in each of thefirst and second states will be specifically described with reference toFIG. 7. Since the linking portions 23 and 24 show the same deformation,only the linking portion 23 will be representatively described. Thedescription of the linking portion 24 is omitted.

In the first state, an end portion, adjacent to the driving member 233,of the elastic member 234 in its longitudinal direction is displacedupwardly while an end portion, adjacent to the driving member 233, ofthe elastic member 235 in its longitudinal direction is displaceddownwardly since the piezoelectric element 55 is elongated while thepiezoelectric element 56 is contracted.

As a result, one portion, adjacent to the elastic member 234 relative tothe rotation center axis X, of the driving member 233 is displacedupwardly while the other portion, adjacent to the elastic member 235relative to the rotation center axis X, of the driving member 233 isdisplaced downwardly. Consequently, the driving member 233 is tiltedabout the rotation center axis X.

On the other hand, in the second state, an end portion, adjacent to thedriving member 233, of the elastic member 234 in its longitudinaldirection is displaced downwardly while an end portion, adjacent to thedriving member 233, of the elastic member 235 in its longitudinaldirection is displaced upwardly since the piezoelectric element 55 iscontracted while the piezoelectric element 56 is elongated.

As a result, one portion, adjacent to the elastic member 234 relative tothe rotation center axis X, of the driving member 233 is displaceddownwardly while the other portion, adjacent to the elastic member 235relative to the rotation center axis X, of the driving member 233 isdisplaced upwardly. Consequently, the driving member 233 is tilted aboutthe rotation center axis X.

The driving member 233 is rotated by repeating the first and secondstates as described above. The rotation of the driving member 233 twiststhe axial member 231 to rotate the movable plate 21.

The third embodiment can also achieve the same effects of the firstembodiment.

Fourth Embodiment

Next, an actuator according to a fourth embodiment of the invention willbe described.

FIG. 10 is a top view illustrating the actuator of the fourthembodiment. FIG. 11 is a sectional view taken along the line D-D in FIG.10.

The following description of an actuator 1C of the fourth embodimentfocuses primarily on differences from the actuator 1B of the thirdembodiment, and similar points will be omitted.

The actuator 1C of the fourth embodiment is nearly the same as theactuator 1B of the third embodiment except for the structure of a base2C, the shape of the support substrate 3, and arrangements of thepiezoelectric elements 55C to 58C. The same numeral is given to the samestructure of the third embodiment.

The base 2C includes a movable plate 21C, a linking portion 23C linkingthe movable plate 21C and each of the piezoelectric elements 55C and56C, and a linking portion 24C linking the movable plate 21C and each ofthe piezoelectric elements 57C and 58C.

The linking portion 23C includes a driving member 233C disposed apartfrom the movable plate 21C, an axial member 231C linking the drivingmember 233C and the movable plate 21C, an elastic member 234C linkingthe driving member 233C and the piezoelectric element 55C and an elasticmember 235C linking the driving member 233C and the piezoelectricelement 56C.

Likewise, the linking portion 24C includes a driving member 243Cdisposed apart from the movable plate 21C, an axial member 241C linkingthe driving member 243C and the movable plate 21C, an elastic member244C linking the driving member 243C and the piezoelectric element 57Cand an elastic member 245C linking the driving member 243C and thepiezoelectric element 58C.

The support substrate 3C has a plate shape. On the upper surface, eachof the piezoelectric elements 55C to 58C is bonded.

The piezoelectric element 55C is disposed so that one end thereof is onthe upper surface of the support substrate 3C while the other endthereof is on and faces an end, opposite to the driving member 233C inthe longitudinal direction of the elastic member 234C, of the elasticmember 234C, as shown in FIG. 11. The piezoelectric element 55C iselongated and contracted in the thickness direction of the movable plate21C. The piezoelectric element 55C is bonded to the support substrate 3Cwith the one end surface (a lower end surface) in theelongation-contraction direction, and also bonded to an end, opposite tothe driving member 233C in the longitudinal direction of the elasticmember 234C, of the elastic member 234C with the other end surface (anupper end surface). That is, the piezoelectric element 55C is providedso as to link the elastic member 234C and the support substrate 3C inthe elongation-contraction direction.

The piezoelectric elements 56C to 58C are disposed on the upper surfaceof the support substrate 3C in the same manner of the piezoelectricelement 55C. That is, the piezoelectric element 56C is provided so as tolink the elastic member 235C and the support substrate 3C in itselongation-contraction direction, the piezoelectric element 57C isprovided so as to link the elastic member 244C and the support substrate3C in its elongation-contraction direction, and the piezoelectricelement 58C is provided so as to link the elastic member 245C and thesupport substrate 3C in its elongation-contraction direction.

Each of the piezoelectric elements 55C to 58C is elongated andcontracted by an energization, thereby rotating the movable plate 21C.Voltage is applied to the piezoelectric elements 55C to 58C to rotatethe movable plate 21C in the same manner of the third embodiment. Thus,the explanation is omitted.

As described above, it can be said that the piezoelectric elements 55Cto 58C serve as a driving source and a supporter to support the base 2C.Since the piezoelectric elements 55C to 58C serve as the supporter tosupport the base 2C, the actuator 1C can be miniaturized.

The actuator 1C of the fourth embodiment may be provided with a frameformed so as to surround the circumference of the base 2C.

The fourth embodiment can also achieve the same effects of the firstembodiment.

Fifth Embodiment

Next, an actuator according to a fifth embodiment of the invention willbe described.

FIG. 12 is a top view illustrating the actuator of the fifth embodiment.

The following description of an actuator 1D of the fifth embodimentfocuses primarily on differences from the actuator 1 of the firstembodiment, and similar points will be omitted.

The actuator 1D of the fifth embodiment is nearly the same as theactuator 1 of the first embodiment except for the arrangements of theelastic members 234D, 235D, 244D, and 245D. The same numeral is given tothe same structure of the first embodiment.

Since a pair of the elastic members 234D and 235D, and a pair of elasticmembers 244D and 245D are symmetrically disposed relative to the movableplate 21 in the plan view of the movable plate 21, only the pair of theelastic members 234D and 235D will be representatively described. Thedescription of the pair of elastic members 244D and 245D is omitted.

The pair of elastic members 234D and 235D is disposed so that aseparation distance L₁ gradually increases from a side adjacent to themovable plate 21 to a side adjacent to the driving member 233. As aresult, the length of each of the elastic members 234D and 235D in thelongitudinal direction can be set longer than that set in a case wherethe pair of elastic members 234D and 235D extends in a direction inparallel with the rotation center axis X (i.e. the first embodiment).Consequently, the driving member 233 can provide a larger swing angle(rotation angle) while the actuator 1 is miniaturized.

In addition, the response of the driving member 233 can be improvedsince the pair of elastic members 234D and 235D can be connected to anend portion, located far from the rotation center axis X, of the drivingmember 233 in the plan view of the movable plate 21.

The fifth embodiment can also achieve the same effects of the firstembodiment.

Sixth Embodiment

Next, an actuator according to a sixth embodiment of the invention willbe described.

FIG. 13 is a top view illustrating the actuator of the sixth embodiment.

The following description of an actuator 1E of the sixth embodimentfocuses primarily on differences from the actuator 1 of the firstembodiment, and similar points will be omitted.

The actuator 1E of the sixth embodiment is nearly the same as theactuator 1 of the first embodiment except for the structures of thelinking portions 23E and 24E. The same numeral is given to the samestructure of the first embodiment.

Since the linking portions 23E and 24E have the same structure, thelinking portion 23E will be representatively described. The descriptionof the linking portion 24E is omitted.

The linking portion 23E includes a driving member 233E disposed apartfrom the movable plate 21, the axial member 231 linking the drivingmember 233E and the movable plate 21, and a pair of elastic members 234Eand 235E linking the driving member 233E and the supporter 22.

The pair of elastic members 234E and 235E is disposed so that aseparation distance L₂ gradually decreases from a side adjacent to themovable plate 21 to a side adjacent to the driving member 233. As aresult, the length of each of the elastic members 234E and 235E in thelongitudinal direction can be set longer than that set in a case wherethe pair of elastic members 234E and 235E extends in a direction inparallel with the rotation center axis X (i.e. the first embodiment),for example. That is, the elastic members 234E and 235E can provide alarger bending deformation amount. Consequently, the driving member 233Ecan provide a larger swing angle (rotation angle) while the actuator 1is miniaturized.

In addition, the separation distance between the border portion of thedriving member 233E and the elastic member 234E, and the border portionof the driving member 233E and the elastic member 235E can be setsmaller than that of the actuator 1 of the first embodiment. As aresult, the driving member 233E can provide a larger rotation angle,thereby increasing the rotation angle of the movable plate 21.

The sixth embodiment can also demonstrate the same effects of the firstembodiment.

Seventh Embodiment

Next, an actuator according to a seventh embodiment of the inventionwill be described.

FIG. 14 is a top view illustrating the actuator of the seventhembodiment. FIG. 15 is a sectional view taken along the line E-E in FIG.14. In the following description, for expository convenience, the topside in FIGS. 14, 15A and 15B is described as “up,” while the bottomside is described as “down or low.”

The following description of an actuator 1F of the seventh embodimentfocuses primarily on differences from the actuator 1 of the firstembodiment, and similar points will be omitted.

The actuator 1F of the seventh embodiment is nearly the same as theactuator 1 of the first embodiment except for the structures of thereturned portions 232F and 242F. The same numeral is given to the samestructure of the first embodiment.

The returned portions 232F and 242F are symmetrically disposed relativeto the movable plate 21 as shown in FIG. 14.

The returned portion 232F includes a driving member 233F connected tothe left end of the axial member 231, a first elastic member 235Flinking the driving member 233F and the protrusion 223, and a secondelastic member 234F linking the driving member 233F and the protrusion222.

Likewise, the returned portion 232F includes a driving member 243Fconnected to the right end of the axial member 231, a first elasticmember 245F linking the driving member 243F and the protrusion 225, anda second elastic member 244F linking the driving member 243F and theprotrusion 224.

The actuator 1F includes a pair of piezoelectric elements 51F and 52F.The piezoelectric element 51F is bonded to the first elastic member 235Fwhile the piezoelectric element 52F is bonded to the first elasticmember 245F.

In the actuator 1F, the piezoelectric elements 51F and 52F are driven tobend the first elastic members 235 f and 245F, respectively. Eachdeformation twists the respective second elastic members 234F and 244Fto rotate the driving members 233F and 234F, respectively. The rotationsof the driving members 233F and 243F give a distortional moment to therespective axial members 231 and 241.

Each of the driving members 233F and 243F has an elongated shapeextending in a direction in parallel with the plate surface of themovable plate 21 and perpendicular to the rotation center axis X. Thedriving member 233F is connected to the axial member 231 at a positionthereof located upper side from the center in its longitudinal directionwhile the driving member 243F is connected to the axial member 241 at aposition thereof located upper side from the center in its longitudinaldirection.

Each of the first elastic members 235F and 245F is designed to mainlyprovide a bending deformation, and has an elongated shape extending in adirection nearly in parallel with the rotation center axis X. The firstelastic members 235F and 245F are disposed at the lower side relative tothe rotation center axis X in FIG. 14.

The first elastic member 235F is capable of being elastically deformed.The right end is fixed to the protrusion 223 while the left end islinked to the lower end portion of the driving member 233F. Likewise,the first elastic member 245F is capable of being elastically deformed.The left end is fixed to the protrusion 225 while the right end islinked to the lower end portion of the driving member 243F.

On the other hand, each of the second elastic members 234F and 244F isdesigned to mainly provide a twisted deformation, and has an elongatedshape extending in a direction nearly in parallel with the rotationcenter axis X. The width of the second elastic member 234F is smallerthan that of the first elastic member 235F while the width of the secondelastic member 244F is smaller than that of the first elastic member245F so that each of the second elastic members 234F and 244F is easilytwisted.

The second elastic members 234F and 244F are disposed at the upper siderelative to the rotation center axis X in FIG. 14. In addition, thesecond elastic members 234F and 244F are disposed in the vicinity of therotation center axis X.

The second elastic member 234F is capable of being elastically deformed.The right end is fixed to the protrusion 222 while the left end islinked to the upper end portion of the driving member 233F. Likewise,the second elastic member 244F is capable of being elastically deformed.The left end is fixed to the protrusion 224 while the right end islinked to the upper end portion of the driving member 243F.

The first elastic member 235F and the second elastic member 234F aredisposed at a side adjacent to the movable plate 21 relative to thedriving member 233F (i.e. inwardly from the driving member 233F) whilethe first elastic member 245F and the second elastic member 244F aredisposed at a side adjacent to the movable plate 21 relative to thedriving member 243F (i.e. inwardly from the driving member 243F).

In the returned portion 232F, the separation distance of the firstelastic member 235F and the axial member 231 (L3 in FIG. 14) is largerthan the separation distance of the second elastic member 234F and theaxial member 231 (L4 in FIG. 14).

Likewise, in the returned portion 242F, the separation distance of thefirst elastic member 245F and the axial member 241 is larger than theseparation distance of the second elastic member 244F and the axialmember 241.

The piezoelectric element 51F is bonded on the first elastic member235F, and is elongated and contracted in its longitudinal direction. Onthe other hand, the piezoelectric element 52F is bonded on the firstelastic member 245F, and is elongated and contracted in its longitudinaldirection. As can be seen from the above arrangement, the piezoelectricelements 51F and 52F are eccentrically located at one side of therotation center axis X (the lower side in FIG. 14).

Since the piezoelectric elements 51F and 52F have the same structure ofthe piezoelectric element 52 described in the first embodiment, thedescription on them is omitted.

The actuator 1F structured as described above is driven by the followingmanner as an example. Since the actuator 1F has a symmetric structurerelative to the movable plate 21, the left portion of the actuator 1F(i.e., the returned portion 232F) will be representatively describedbelow.

A periodically changing voltage is applied to the piezoelectric element51F to operate the actuator 1F. The voltage may be alternating currentor intermittent direct current, for example.

Since the piezoelectric elements 51F and 52F are eccentrically locatedat one side of the rotation center axis X as described above, voltage isapplied to each of the piezoelectric elements 51F and 52F so that thepair of piezoelectric elements 51F and 52F is elongated and contractedwith the same timing. As a result, driving circuits and power supplysources (not shown) to drive the piezoelectric elements 51F and 52F canbe simply structured.

In addition, voltage applied to each of the piezoelectric elements 51Fand 52F preferably periodically changes with a frequency equal to theresonance frequency of a twist vibrator composed of the movable plate 21and the pair of axial members 231 and 241. The voltage allows themovable plate 21 to provide a large rotation angle while the deformationamounts of the first elastic members 235F and 245F, the second elasticmembers 234F and 244F, the driving members 233F and 243F, and thepiezoelectric elements 51F and 52F are suppressed. That is, the movableplate 21 can provide a larger rotation angle with a low power drive.

With such voltage applied, the piezoelectric element 51F is elongatedand contracted in its longitudinal direction (the longitudinal directionof the first elastic member 235F). That is, the piezoelectric elements51F alternately repeats the elongation state and the contraction statewith the voltage frequency.

More specifically, the piezoelectric element 51F is in the contractionstate as shown in FIG. 15A when no voltage is applied. In the state, thefirst elastic member 235F is not bent (not bent downwardly), and thesecond elastic member 234F is not also twisted. In contrast, thepiezoelectric element 51F is in the elongation state as shown in FIG.15B when voltage is applied. In the state, the first elastic member 235Fis bent downwardly. The deformation of the first elastic member 235Finduces the displacement of the left end portion of the driving member233F in FIGS. 15A and 15B. In this case, the position of the right endportion of the driving member 233F is mostly unchanged since the rightend portion of the driving member 233F is supported by the secondelastic member 234F. As a result, the driving member 233F is tilted(displaced) as shown in FIG. 15B. When no voltage is applied to thepiezoelectric element 51F in the duration in which the piezoelectricelement 51F alternately repeats the elongation state and the contractionstate with a predetermined period, the second elastic member 234F istwisted in the direction opposite to that shown in FIG. 15B by anreactive force of the second elastic member 234F twisted and the firstelastic member 235F bent, and the first elastic member 235F is bentupwardly.

The posture change of the driving member 233F induces the posture tiltof the axial member 231 in its traverse plane. As a result, distortionaltorque is given to the axial member 231.

With the distortional torque, the axial member 231 is twisted to rotatethe movable plate 21 about the rotation center axis X.

The actuator 1F can reduce the number of parts used other than the sameeffects of the actuator 1 of the first embodiment since singlepiezoelectric element gives distortional torque to each of the axialmembers 231 and 241 to rotate the movable plate 21 with suppressing theshift of the rotation center axis X.

Particularly, the shift of the rotation center axis X of the movableplate 21 can be prevented even when a driving force is applied to onlyone side of each of the driving members 233F and 243F relative to therotation center axis X (the lower side of FIG. 14) since the rotationcenter axis X is positioned in the vicinity of each of the secondelastic members 234F and 244F that are twisted. Since the necessarynumber of piezoelectric elements to rotate the movable plate 21 (in theembodiment, two pieces: the piezoelectric elements 51F and 52F) issmall, the actuator 1F can be provided at low costs. Because of thesmall number of piezoelectric elements, it becomes simple to smoothlyrotate the movable plate 21 with a little influence of a fixing positionshift or dimension error of each piezoelectric element.

In addition, the rotation center axis X of the movable plate 21 can alsobe prevented from being shifted from the following point of view. Eachof the second elastic members 234F and 244F is twisted (mainlydistortional deformation) and each of the first elastic members 235F and245F is bent (mainly bending deformation) when each of the drivingmembers 233F and 243F rotates.

Further, the rotation center axis X of the movable plate 21 can also beprevented from being shifted with the pair of axial members 231 and 241having a simplified shape since each of the second elastic members 234Fand 244F is disposed in the vicinity of the rotation center axis X.

The embodiments of the actuator have been described above. The actuatorcan be used for MEMS applied sensors such as acceleration sensors andangular velocity sensors, and optical devices such as optical scanners,optical switches, and optical attenuators.

An optical scanner of the invention has a similar structure of theactuator. Since embodiments of the optical scanner are similar to theembodiments described above, detailed descriptions are omitted. Theoptical scanner can be preferably applied to image forming devices suchas projectors, laser printers, displays for imaging, barcode readers,and confocal scanning microscopes. As a result, image forming deviceshaving superior imaging characteristics can be provided.

A projector 9 shown in FIG. 16 will be specifically described. Forexpository convenience, the longitudinal direction of a screen S isdenoted as a “horizontal direction” and a direction perpendicular to thelongitudinal direction is denoted as a “vertical direction”.

The projector 9 includes a light source device 91 emitting light such asa laser beam, a cross dichroic prism 92, a pair of optical scanners 93and 94 of the invention (e.g. optical scanner having a similar structureof the actuator 1), and a fixed mirror 95.

The light source device 91 is provided with a red light source device911 emitting a red light component, a blue light source device 912emitting a blue light component, and a green light source device 913emitting a green light component.

The cross dichoric prism 92, which is composed of four right angleprisms bonded together, combines a light component emitted from each ofthe red light source device 911, the blue light source device 912, andthe green light source device 913.

In the projector 9, a light component emitted from each of the red lightsource device 911, the blue light source device 912, and the green lightsource device 913 based on image information from a host computer (notshown) is combined by the cross dichonic prism 92. The combined light isscanned by the optical scanners 93 and 94 and then reflected by thefixed mirror 95 to form a color image on the screen S.

The optical scan by the optical scanners 93 and 94 is specificallydescribed.

The light combined by the cross dichonic prism 92 is scanned in thehorizontal direction by the optical scanner 93 (main scan). Then, thehorizontally scanned light is scanned in the vertical direction by theoptical scanner 94 (sub scan). As a result, a two-dimensional colorimage can be formed on the screen S. The optical scanners 93 and 94 canprovide extremely superior imaging characteristics.

The structure of the projector 9 is not limited to one described aboveas long as it is structured to scan light by an optical scanner to forman image to an object. For example, the fixed mirror 95 may be omitted.

While the actuator, the optical scanner, and the image forming device ofthe invention are described based on the illustrated embodiments thusfar, but the invention is not limited to those embodiments. For example,the actuator, the optical scanner, and the image forming device of theinvention may include any substitute that has the same function as itsoriginal structure and may include any additional structure.

While the actuator has a nearly symmetric structure relative to themovable plate 21 in the embodiments described above, it may have anasymmetric structure.

In addition, while the returned portion includes the driving member anda pair of elastic members in the embodiments described above, thestructure is not limited to this as long as it can tolerate theelongation of the axial member due to thermal expansion and reduce itsdisplacement in the thickness direction of the movable plate. Forexample, the returned portion may include the pair of the elasticmembers without employing the driving member. In this case, each elasticmember links the ends portion of the axial member and the supporter.Further, it is not necessary that the elastic member be provided in apair. Single elastic member may be provided. More than two elasticmembers may be provided.

1. An actuator, comprising: a movable plate; a supporter to support themovable plate; a pair of linking portions to link the movable plate andthe supporter so as to allow the movable plate to rotate relative to thesupporter; and a piezoelectric element to rotate the movable plate,wherein the piezoelectric element elongated and contracted by anenergization twists the pair of linking portions to rotate the movableplate; each of the pair of the linking portions includes: an axialmember extending from the movable plate, a driving member connected tothe axial member, and a pair of elastic members capable of beingelastically deformed connected to opposing ends of the driving member,each elastic member having a first end connected to the driving memberand a second end that is closer to the movable plate than the first end,each elastic member extending from the first end axially back toward themovable plate to the second end, wherein each of the pair of elasticmembers faces each other across a rotation center axis of the movableplate.
 2. The actuator according to claim 1, wherein each of the pair ofelastic members has an elongation shape and a longitudinal direction ofeach of the elastic members is in parallel with the rotation center axisof the movable plate.
 3. The actuator according to claim 1, wherein eachof the pair of elastic members includes a first elastic member and asecond elastic member having a separation distance smaller than aseparation distance of the first elastic element relative to the axialmember, and the piezoelectric element is bonded to the first elasticmember, and an elongation-contraction of the piezoelectric element in alongitudinal direction of the first elastic member bends the firstelastic member to twist the second elastic member to displace thedriving member.
 4. The actuator according to claim 3, wherein the secondelastic member is provided in a vicinity of the rotation center axis. 5.The actuator according to claim 1, wherein each of the pair of elasticmembers has an elongation shape and a separation distance between thepair of elastic members gradually decreases from a side adjacent to themovable plate to a side adjacent to the driving member.
 6. The actuatoraccording to claim 1, wherein each of the pair of elastic members has anelongation shape and a separation distance between the pair of elasticmembers gradually increases from a side adjacent to the movable plate toa side adjacent to the driving member.
 7. The actuator according toclaim 1, wherein each of the pair of elastic members has an elongationshape and the piezoelectric element is bonded to each of the elasticmembers in a longitudinal direction of each of the elastic members andis elongated and contracted in the longitudinal direction to bend eachof the elastic members.
 8. The actuator according to claim 7, whereineach piezoelectric element has a width larger than a width of each ofthe elastic members and is bonded so as to entirely cover each of theelastic members in a width direction of each of the elastic members. 9.The actuator according to claim 1, wherein the piezoelectric element isprovided to correspond to each of the elastic members, and an end in anelongation-contraction direction of each piezoelectric element toucheseach of corresponding elastic members, and an elongation-contraction ofeach piezoelectric element bends each of the elastic members.
 10. Theactuator according to claim 9, wherein each of the pair of elasticmembers has an elongation shape and each piezoelectric element is bondedto an end in an elongation direction of each of the correspondingelastic members and serves as the supporter, and the end is located at aside opposite to the driving member.
 11. The actuator according to claim1, wherein the movable plate has a light reflector having lightreflection property on a plate surface thereof.
 12. An optical scanner,comprising: a movable plate provided with a light reflector having lightreflection property; a supporter to support the movable plate; a pair oflinking portions to link the movable plate and the supporter so as toallow the movable plate to rotate relative to the supporter; and apiezoelectric element to rotate the movable plate, wherein thepiezoelectric element elongated and contracted by an energization twiststhe pair of linking portions to rotate the movable plate to scan lightreflected by the light reflector; each of the linking portions includes:an axial member extending from the movable plate, a driving memberconnected to the axial member, and a pair of elastic members capable ofbeing elastically deformed connected to opposing ends of the drivingmember, each elastic member having a first end connected to the drivingmember and a second end that is closer to the movable plate than thefirst end, each elastic member extending from the first end axially backtoward the movable plate to the second end, wherein each of the pair ofelastic members faces each other across a rotation center axis of themovable plate.
 13. An image forming device, comprising: an opticalscanner including: a movable plate provided with a light reflectorhaving light reflection property; a supporter to support the movableplate; a pair of linking portions to link the movable plate and thesupporter so as to allow the movable plate to rotate relative to thesupporter; and a piezoelectric element to rotate the movable plate,wherein the piezoelectric element elongated and contracted by anenergization twists the pair of linking portions to rotate the movableplate to scan light reflected by the light reflector; each of thelinking portions includes: an axial member extending from the movableplate, a driving member connected to the axial member, and a pair ofelastic members capable of being elastically deformed connected toopposing ends of the driving member, each elastic member having a firstend connected to the driving member and a second end that is closer tothe movable plate than the first end, each elastic member extending fromthe first end axially back toward the movable plate to the second end,wherein each of the pair of elastic members faces each other across arotation center axis of the movable plate.
 14. An actuator, comprising:a movable plate; a supporter to support the movable plate; a pair oflinking portions to link the movable plate and the supporter so as toallow the movable plate to rotate relative to the supporter; and apiezoelectric element to rotate the movable plate, wherein thepiezoelectric element elongated and contracted by an energization twiststhe pair of linking portions to rotate the movable plate; each of thepair of the linking portions includes: an axial member extending fromthe movable plate, a driving member connected to the axial member, and apair of elastic members capable of being elastically deformed connectedto opposing ends of the driving member and extending between the movableplate and the driving member, wherein each of the pair of elasticmembers faces each other across a rotation center axis of the movableplate.